In recent years, in mobile terminals or other communication apparatuses, acoustic wave elements have been used in the filters filtering the signals which are transmitted to and received from their antennas. An acoustic wave element is configured by a piezoelectric substrate and an excitation electrode formed on a major surface of the piezoelectric substrate. The filter utilizes the characteristic that an electrical signal and a surface acoustic wave can be converted to each other due to the relationship between the excitation electrode and the piezoelectric substrate.
Japanese Patent Publication No. 5-183380A discloses a filter configured by connecting a plurality of acoustic wave elements in a ladder type.